This invention relates to a bent pipe or elbow used at a corner portion of an airconditioning duct, an exhaust pipe, a drain pipe or the like to connect pipe sections.
A bent pipe made by helically winding a metal strip and fastening together folded portions extending along its adjacent edges is disclosed in Japanese Examined Patent Publications 59-27478 and 63-50595. Such a pipe is made from a metal strip having wide and narrow portions arranged alternately so that both side edges thereof will delineate moderately curved lines in a symmetrical relation. In making a metal strip having such a shape from a metal plate, edge portions are wasted. This contributes to the cost of the end product.